As defined herein, a "subscriber" is a communication system user. "Subscriber traffic" is defined herein as data originating from one or more communication devices operated by one or more subscribers. The subscriber traffic-carrying capacity of a communications system is limited, because a finite quantity of resources (e.g., electrical energy stored in a satellite battery, or channel capacity of a radio link) exists within any communication system. Correspondingly, the number of subscribers who may access the communication system at one time is also limited. When subscriber traffic exceeds the capacity of the communication system, some subscribers will be denied access. Frequent denial of access is likely to result in unsatisfied subscribers.
In any system with finite resources, management of the system resources is desirable to provide better system performance (e.g., more subscriber traffic-carrying capacity) than if resource management were not performed at all.
Prior art ground-based (non-cellular) communication systems (e.g., a telephone network) generally contain communication nodes (e.g., telephones or radios) utilized by subscribers, a central control facility which manages overall operation of the system, and distribution devices which control subscriber traffic based on instructions from the central control facility. One function of the central control facility may be to control the amount of subscriber traffic through the system. Prior art distribution management may be done in a reactive manner (i.e., the control facility adjusts assignment instructions in real-time by reacting to actual quantities of subscriber traffic), or it may be done in a predictive manner (i.e., the control facility predicts future quantities of subscriber traffic, and instructs distribution devices to control future subscriber traffic based on the prediction).
Prior art ground-based cellular communication systems also contain communication nodes (e.g., cellular telephones), distribution devices, and a central control facility. However, central control facilities for prior art ground-based cellular communications systems do not manage subscriber traffic in a predictive manner. They merely react to subscriber traffic demand in real-time. When subscriber traffic demand exceeds the capacity of the system, users will be denied access to the system.
Non-cellular and cellular distribution devices typically have a fixed set of communication nodes to service. Non-cellular distribution devices service communication nodes that are generally coupled to the specific distribution device through some static transmission medium. Cellular distribution devices service communication nodes that are located within a fixed geographical area within communication range of the particular distribution device.
As communication needs grow, satellite-based cellular communication systems have become a desirable alternative to prior an ground-based non-cellular and cellular communication systems. Unlike prior art ground-based systems, satellite-based communication systems may readily provide world-wide communication coverage. Distribution devices associated with satellite-based cellular communication systems (i.e., satellites) differ from distribution devices of ground-based communication systems in two ways.
First, satellites may not service a fixed quantity of subscribers. For non-geostationary satellites, the satellites move with respect to the surface of the earth. Thus, the geographical area and the number of subscribers seen by a satellite may vary dramatically with the changing location of the satellite.
Second, the resources of satellite cellular distribution devices are highly dynamic. Weight and size constraints limit the quantity of resources each satellite may contain at launch. Additionally, resources are difficult to increase or replenish due to the remoteness of the satellites. Accordingly, each satellite may have a completely different set of rules and constraints from every other satellite, and the overall state of the system may never repeat.
Adequate resource management depends on a robust prediction of subscriber traffic which the satellites will encounter. Such a prediction would allow the communication system to knowledgeably limit subscriber access over a particular region while still providing acceptable service to the region and other geographical areas over which the satellite subsequently passes.
Thus, what is needed is a method and apparatus for predicting subscriber traffic demand for a communication system so that the resources used may be controlled in a manner to allow the system to handle subscriber traffic efficiently. Particularly needed is a system and method for predicting subscriber traffic demand for a satellite cellular communication system containing limited, dynamic resources where subscriber traffic demand varies.